Ultrafast coherent control in the electronic ground state of a molecule

We report on a coherent control experiment to selectively excite a well loc alized nuclear probability density in the electronic ground state of isolat ed, jet cooled potassium dimer molecules. The basic idea of this control sc heme is to take advantage of the motion of a vibrational wave packet create d in an intermediate excited electronic state, from which a Franck-Condon w indow to the desired final state in the ground state emerges. To realize th is concept we apply a resonant stimulated Raman process, in which the two i nvolved laser pulses are separated by a time delay tau(1) and their wavelen gths are independently tunable. The method enables us to excite ground stat e vibrational wave packets, whereby the vibrational energy of the wave pack et and the position of its generation along the internuclear separation coo rdinate of the ground state potential energy surface can in principle be fr eely chosen by the experimentalist. The results we present for the chosen m odel system K-2 strongly support the idea that this control concept might b e one possible approach to selectively populate a desired chemical reaction channel in the electronic ground state of a molecule.